The Sylvester Allochthon: upper Paleozoic marginal-basin and island-arc terranes in northern British Columbia

1993 ◽  
Vol 30 (3) ◽  
pp. 631-643 ◽  
Author(s):  
JoAnne L. Nelson
Keyword(s):  
North America ◽  
Deep Water ◽  
Island Arc ◽  
Upper Permian ◽  
Structural Level ◽  
Division Iii ◽  
Crust And Upper Mantle ◽  
Marginal Basin ◽  
Upper Paleozoic ◽  
Division Ii

The Sylvester Allochthon is a composite klippe of upper Paleozoic ophiolitic, island-arc, and pericratonic assemblages, which rests directly on the Cassiar terrane, a displaced sliver of Ancestral North America. Each tectonic assemblage occurs at a distinct and consistent structural level within the allochthon. They are assigned, respectively, to the Slide Mountain, Harper Ranch, and Yukon–Tanana terranes. The Sylvester Allochthon provides a view of the structural relationships between these terranes prior to Early Cretaceous – early Tertiary strike-slip dismemberment, as well as possible sedimentological links to late Paleozoic North America. Slide Mountain Terrane assemblages, designated divisions I and II, form the lowest structural panels. Chert – quartz sandstones are interbedded with Lower Mississippian deep-water sediments in division I and ocean-floor basalts and deep-water sediments in division II. They are similar in age and character to sandstones in the autochthonous Earn Group. Division II assemblages represent atypical oceanic crust and upper mantle assemblages. Continuous basalt–sedimentary sequences, well dated by conodont faunas, span Early Mississippian to mid-Permian time. Feeders for the basalts are sills rather than sheeted dyke swarms, suggesting very slow spreading and high(?) sedimentation rates in a marginal-basin setting. These supracrustal sequences are thrust-imbricated with ultramafite–gabbro panels. Division II is in part overlain by a Triassic siliciclastic and limy sedimentary sequence, which resembles the basal Takla Group, Slocan Group, and autochthonous Triassic units. Division III occupies the highest structural levels in the allochthon. With one exception, thrust sheets within it consist of Pennsylvanian to Upper Permian mixed calc-alkaline volcanic and plutonic rocks, chert, tuff, and limestone, assigned to the Harper Ranch Terrane. One panel, assigned to the Yukon–Tanana Terrane, consists of an Early Mississippian quartz diorite pluton with Precambrian inheritance that intrudes older volcanogenic sediments, pyroclastics, limestone, and siliciclastic sediments. Preferred pre-Mesozoic restoration of these terrane elements shows a Harper Ranch arc, built partly on pericratonic Yukon–Tanana and partly on primitive oceanic basement (division III), which is separated from North America by the Slide Mountain marginal basin (divisions I and II).

Geochemical discrimination between ocean-floor and island-arc tholeiites—application to some ophiolites

1979 ◽  
Vol 16 (9) ◽  
pp. 1874-1882 ◽  
Author(s):  
L. Beccaluva ◽  
D. Ohnenstetter ◽  
M. Ohnenstetter
Keyword(s):  
North America ◽  
Oceanic Crust ◽  
Island Arc ◽  
The Other ◽  
Ocean Floor ◽  
Oceanic Ridge ◽  
Marginal Basin ◽  
Discrimination Diagram ◽  
The Mediterranean ◽  
Arc Setting

Two discriminative diagrams are proposed to separate island-arc tholeiites (1AT) and ocean-floor tholeiites (OFT). The first diagram, Ti/Cr vs. Ni, has been drawn using 84 island-arc (IAT) and 178 ocean-floor (OFT) samples with silica contents between 40 and 56%. About 97% of OFT and 93% of IAT samples fall, respectively, on opposite sides of the empirical boundary. In the second diagram, where the Ba/Y is less than 4.4 for the OFT and more than 3.9 for the IAT, the overlap between the two groups is about 6%.Owing to alteration effects, only the discrimination diagram Ti/Cr vs. Ni has been applied to ophiolitic basalts from the Mediterranean belts, Newfoundland, Central and North America, and Mongolia. The effusive and hypabyssal formations plotting either in one group or in the other lead to the suggestion that they have been formed in several possible geotectonical environments. It appears that ophiolites generated in a mid-oceanic ridge are scarce in opposition to those formed in an island-arc setting. In this latter case, ophiolite associations may correspond to the juxtaposition of either island-arc – marginal basin or island-arc – offshore oceanic crust formations.

The rise and fall of late Paleozoic trilobites of the United States

1999 ◽  
Vol 73 (2) ◽  
pp. 164-175 ◽  
Author(s):  
David K. Brezinski
Keyword(s):  
United States ◽  
North America ◽  
Sea Level ◽  
Adaptive Radiation ◽  
The United States ◽  
Upper Permian ◽  
Late Paleozoic ◽  
Lower Permian ◽  
Stage 4 ◽  
Stage 1

Based on range data and generic composition, four stages of evolution are recognized for late Paleozoic trilobites of the contiguous United States. Stage 1 occurs in the Lower Mississippian (Kinderhookian-Osagean) and is characterized by a generically diverse association of short-ranging, stenotopic species that are strongly provincial. Stage 2 species are present in the Upper Mississippian and consist of a single, eurytopic, pandemic genus, Paladin. Species of Stage 2 are much longer-ranging than those of Stage 1, and some species may have persisted for as long as 12 m.y. Stage 3 is present within Pennsylvanian and Lower Permian strata and consists initially of the eurytopic, endemic genera Sevillia and Ameura as well as the pandemic genus Ditomopyge. During the middle Pennsylvanian the very long-ranging species Ameura missouriensis and Ditomopyge scitula survived for more than 20 m.y. During the late Pennsylvanian and early Permian, a number of pandemic genera appear to have immigrated into what is now North America. Stage 4 is restricted to the Upper Permian (late Leonardian-Guadalupian) strata and is characterized by short-ranging, stenotopic, provincial genera.The main causal factor controlling the four-stage evolution of late Paleozoic trilobites of the United States is interpreted to be eustacy. Whereas Stage 1 represents an adaptive radiation developed during the Lower Mississippian inundation of North America by the Kaskaskia Sequence, Stage 2 is present in strata deposited during the regression of the Kaskaskia sea. Stage 3 was formed during the transgression and stillstand of the Absaroka Sequence and, although initially endemic, Stage 3 faunas are strongly pandemic in the end when oceanic circulation patterns were at a maximum. A mid-Leonardian sea-level drop caused the extinction of Stage 3 fauna. Sea-level rise near the end of the Leonardian and into the Guadalupian created an adaptive radiation of stentopic species of Stage 4 that quickly became extinct with the latest Permian regression.

scholarly journals Impact of Various Collegiate Settings on Athletic Trainers’ Definition of Professional Commitment

2014 ◽  
Author(s):  
Stephine Mazerolle ◽  
Christianne Eason
Keyword(s):  
Athletic Training ◽  
Student Athletes ◽  
Quality Care ◽  
Division I ◽  
Professional Commitment ◽  
Full Time ◽  
Division Iii ◽  
Division Ii ◽  
Definition Of ◽  
The Impact

Purpose: Professional commitment is an individualized concept that combines commitment to a profession and the organization of employment. Currently there is no distinct definition of professional commitment within the context of athletic training. Therefore, the purpose of our study was to evaluate the impact of collegiate divisional setting on the definition of professional commitment. Methods: Online asynchronous interviews. Inclusion criteria consisted of full-time employment in the collegiate setting with at least 1 year of experience beyond a graduate assistantship. Thirty-three BOC certified ATs employed in the collegiate setting (Division I =11, Division II = 9, Division III = 13) volunteered with an average of 10 ± 8 years of clinical experience. Data saturation guided the total number of participants. Participants journaled their thoughts and experiences via QuestionPro™. Multiple analyst triangulation and peer review were included and data was analyzed utilizing general inductive analysis. Results: The importance of current practices emerged across all three settings. ATs in the Division I setting viewed commitment as advocating for their student athletes, providing the best care possible, and mentoring them as young adults. In the Division II setting, ATs were focused on life-long learning as a reflection of commitment. This was often accomplished by attending seminars, completing CEUs, and continually adding to their skill set in order to provide the best care for their student athletes. Division III focused their definition on being a multifaceted health care provider. Exceeding expectations and being a dedicated professional was an aspect of professional commitment. Conclusions: It is important to understand what keeps ATs motivated in the profession in order to enhance retention strategies. Overall, ATs’ professional commitment is derived from providing quality care to student-athletes, continuously advancing education within the profession, and being a multifaceted healthcare provider.

The upper Paleozoic (Pennsylvanian-Permian) ammonoid Emilites

1988 ◽  
Vol 62 (1) ◽  
pp. 69-75 ◽  
Author(s):  
Royal H. Mapes ◽  
Darwin R. Boardman
Keyword(s):  
Soviet Union ◽  
North America ◽  
Species Level ◽  
Time Range ◽  
Early Permian ◽  
Generic Level ◽  
The Soviet Union ◽  
Upper Paleozoic ◽  
Long Time ◽  
Permian Ammonoid

Four species of Emilites are now known; these are E. incertus (Böse), E. plummeri Ruzhencev, E. brownwoodi n. sp., and E. bennisoni n. sp. Representatives of this genus may occur as early as Middle Pennsylvanian in North America to as late as Early Permian in the Soviet Union. All described taxa are from North America except E. plummeri, which is from the Soviet Union. Because Emilites is extremely rare in upper Paleozoic ammonoid assemblages, generic and species level phylogenetic relationships are poorly understood. Emilites is not considered to be a good generic-level zone indicator due to its relatively long time range and its rarity.

scholarly journals IGCP 272 - Late Palaeozoic and Early Mesozoic circum-Pacific events and their global correlation

1992 ◽  
Vol 6 ◽  
pp. 85-85
Author(s):  
J. M. Dickins
Keyword(s):  
North America ◽  
Western Europe ◽  
Important Change ◽  
Upper Permian ◽  
Triassic Boundary ◽  
Early Mesozoic ◽  
The Earth ◽  
Late Palaeozoic ◽  
Global Correlation ◽  
Harsh Climate

IGCP 203 - Permo-Triassic events of eastern Tethys and their intercontinental correlation - focussed on the Permian-Triassic boundary sequences and in particular there was a consensus that the distinctive biological changes were associated with strong sea-level and tectonic change, strong volcanic activity and a harsh climate. These factors were connected with an important change in the environment and with the exception perhaps of the climate, reflected deep-seated changes within the earth. The project also resulted in improving the physical understanding of the sequences and their biostratigraphy and correlation.IGCP 272 was developed, and was approved in 1988, to apply these results to understanding the Late Palaeozoic and Early Mesozoic and was focussed on the Pacific as integration around this region seemed to offer especially fruitful possibilities.Working group meetings up to the end of 1991 have been held in Australia (Newcastle and Hobart), New Zealand (Dunedin), South America (Sao Paulo and Buenos Aires) and North America (Washington). Meetings are planned in North America, Japan, Eastern Siberia or Thailand and western Europe (France-Spain-Austria).Special cooperation has developed with the Carboniferous, Permian and Triassic Subcommissions of IUGS and with IGCP 214 - Global Bio-events. Using the more exact time correlations developed it has now been possible to show that major geological and biological events (of different levels of significance) are associated with major boundaries already recognized in the World Standard Stratigraphical Time Scale. These comprise the Carboniferous-Permian, the mid-Permian (twofold subdivision, the Permian-Triassic (already recognized in earlier work), the Lower-Middle and Middle-Upper Triassic and the Triassic-Jurassic boundaries.A special achievement of the project has been to show the similar significance of the Midian-Dzhulfian boundary within the Upper Permian but corresponding closely to the traditional Lower-Upper Permian of China and the Middle-Upper Permian of Japan.Although there are also other events at levels which have not been investigated by the project, those outlined all seem to reflect important changes within the earth.

scholarly journals The only known cyclopygid–‘atheloptic’ trilobite fauna from North America: the upper Ordovician fauna of the Pyle Mountain Argillite and its palaeoenvironmental significance

2012 ◽  
Vol 149 (6) ◽  
pp. 964-988 ◽  
Author(s):  
ALAN W. OWEN ◽  
DAVID L. BRUTON
Keyword(s):  
New Species ◽  
North America ◽  
Deep Water ◽  
Benthic Fauna ◽  
Taxonomic Diversity ◽  
Relative Depth ◽  
Upper Ordovician ◽  
Brachiopod Fauna ◽  
Depth Ranges ◽  
One New Species

AbstractThe trilobite fauna of the upper Ordovician (middle Katian) Pyle Mountain Argillite comprises a mixture of abundant mesopelagic cyclopygids and other pelagic taxa and a benthic fauna dominated by trilobites lacking eyes. Such faunas were widespread in deep water environments around Gondwana and terranes derived from that continent throughout Ordovician time but this is the only known record of such a fauna from North America and thus from Laurentia. It probably reflects a major sea level rise (the ‘Linearis drowning events’) as does the development of coeval cyclopygid-dominated deep water trilobite faunas in terranes that were marginal to Laurentia and are now preserved in Ireland and Scotland. The Pyle Mountain Argillite trilobite fauna occurs with a deep water Foliomena brachiopod fauna and comprises 22 species. Pelagic trilobites (mostly cyclopygids) constitute 36% of the preserved sclerites, and 45% of the fauna is the remains of trilobites lacking eyes, including one new species, Dindymene whittingtoni sp. nov. Three species of cyclopygid are present, belonging in Cyclopyge, Symphysops and Microparia (Heterocyclopyge). Cyclopygids are widely thought to have been stratified in the water column in life and thus their taxonomic diversity reflects the relative depths of the sea-beds on which their remains accumulated. A tabulation of middle and upper Katian cyclopygid-bearing faunas from several palaeoplates and terranes arranged on the basis of increasing numbers of cyclopygid genera allows an assessment of the relative depth ranges of the associated benthic taxa. The Pyle Mountain Argillite fauna lies towards the deeper end of this depth spectrum.

Nina Creek Group and Lay Range Assemblage, north-central British Columbia: remnants of late Paleozoic oceanic and arc terranes

1997 ◽  
Vol 34 (6) ◽  
pp. 854-874 ◽  
Author(s):  
Filippo Ferri
Keyword(s):  
British Columbia ◽  
North America ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Ocean Floor ◽  
North Central ◽  
Marginal Basin ◽  
The North ◽  
Lower Division ◽  
Ocean Ridge

In north-central British Columbia, a belt of upper Paleozoic volcanic and sedimentary rocks lies between Mesozoic arc rocks of Quesnellia and Ancestral North America. These rocks belong to two distinct terranes: the Nina Creek Group of the Slide Mountain terrane and the Lay Range Assemblage of the Quesnel terrane. The Nina Creek Group is composed of Mississippian to Late Permian argillite, chert, and mid-ocean-ridge tholeiitic basalt, formed in an ocean-floor setting. The sedimentary and volcanic rocks, the Mount Howell and Pillow Ridge successions, respectively, form discrete, generally coeval sequences interpreted as facies equivalents that have been interleaved by thrusting. The entire assemblage has been faulted against the Cassiar terrane of the North American miogeocline. West of the Nina Creek Group is the Lay Range Assemblage, correlated with the Harper Ranch subterrane of Quesnellia. It includes a lower division of Mississippian to Early Pennsylvanian sedimentary and volcanic rocks, some with continental affinity, and an upper division of Permian island-arc, basaltic tuffs and lavas containing detrital quartz and zircons of Proterozoic age. Tuffaceous horizons in the Nina Creek Group imply stratigraphic links to a volcanic-arc terrane, which is inferred to be the Lay Range Assemblage. Similarly, gritty horizons in the lower part of the Nina Creek Group suggest links to the paleocontinental margin to the east. It is assumed that the Lay Range Assemblage accumulated on a piece of continental crust that rifted away from ancestral North America in the Late Devonian to Early Mississippian by the westward migration of a west-facing arc. The back-arc extension produced the Slide Mountain marginal basin in which the Nina Creek Group was deposited. Arc volcanism in the Lay Range Assemblage and other members of the Harper Ranch subterrane was episodic rather than continuous, as was ocean-floor volcanism in the marginal basin. The basin probably grew to a width of hundreds rather than thousands of kilometres.

Timing of events in an Early Cretaceous island arc–marginal basin system on South Georgia

1979 ◽  
Vol 116 (3) ◽  
pp. 167-179 ◽  
Author(s):  
P. W. G. Tanner ◽  
D. C. Rex
Keyword(s):  
Continental Crust ◽  
Island Arc ◽  
Magmatic Arc ◽  
South Georgia ◽  
Marginal Basin ◽  
Early Mesozoic ◽  
Mafic Complex ◽  
Minimum Age ◽  
Radiometric Ages ◽  
Basin System

Summary19 new K–Ar mineral ages of 78-201 Ma and 3 Rb–Sr whole rock isochron ages of 81 ± 10, 127±4 and 181±30 Ma are presented from units of continental crust, mafic complex and island arc assemblage on South Georgia. The Drygalski Fjord Complex, part of the possible floor of the marginal basin in the southern part of the island, includes granodiorite and gabbro plutons of minimum age 180–200 Ma. Together with older metasediments they have been affected by a major thermal event at about 140 Ma, thought to have resulted from the emplacement of a mafic complex (Larsen Harbour Formation) during the initial opening of the marginal basin. Rocks of the Larsen Harbour Formation are cut by the Smaaland Cove intrusion dated by Rb–Sr whole rock isochron at 127±4 Ma. An island arc assemblage exposed to the SW of South Georgia consists of pyroclastic rocks cut by monzodiorite and andesite intrusions, which give radiometric ages of 81–103 Ma. These data suggest that the marginal basin opened during the late Jurassic (pre-140 Ma); that part of an earlier (early Mesozoic) magmatic arc is preserved in continental crust making up part of the floor of the basin; and that subduction continued beneath the island arc until at least the Senonian time. The younger plutons in the arc were emplaced at roughly the same time as turbidite facies rocks at deep levels in the marginal basin were being affected by penetrative deformation and metamorphism. The timing of events on South Georgia agrees closely with that deduced for the continuation of the same island arc–marginal basin system in South America. The 180–200 Ma plutons correlate with an older suite of plutonic rocks reported from the Antarctic Peninsula and southern Andes; they are part of a once-continuous magmatic arc related to subduction of the Pacific plate beneath Gondwanaland during the early Mesozoic.

A Late Mesozoic island arc in the southern Andes, Chile

1979 ◽  
Vol 116 (3) ◽  
pp. 181-190 ◽  
Author(s):  
M. Suárez
Keyword(s):  
Continental Crust ◽  
Rift Zone ◽  
Volcanic Rocks ◽  
Upper Jurassic ◽  
Island Arc ◽  
Volcanic Complex ◽  
Late Mesozoic ◽  
Marginal Basin ◽  
The Pacific ◽  
Pacific Side

SummaryThe Hardy Formation, a sequence of Upper Mesozoic volcanic rocks exposed in Peninsula Hardy (Isla Hoste) in the southernmost archipelago of Chile represents, at least in part, the island-arc assemblage of an island-arc-marginal-basin system related to an eastward dipping subduction zone. This island arc was founded on South American continental crust and is also represented in the island of South Georgia 2000 km to the E. The island-arc assemblage includes pyroclastic rocks, characterized by a high proportion of vitric material, and lava intercalations ranging in composition from rhyolite to basalt. These rocks underwent zeolite and prehnite-pumpellyite facies metamorphism and are gently folded, in contrast with the intense folding exhibited by the rocks exposed to the north of Peninsula Hardy. Silicic volcanics assigned to this assemblage underlie pillow lavas, and are intruded by dolerites and gabbros probably related to a Late Jurassic-Early Cretaceous ophiolite magmatism associated with the generation of a quasioceanic marginal basin. Volcanic turbidites (Yahgan Formation) were deposited into the marginal basin.It is suggested that in pre-marginal basin times the Hardy Formation interfingered towards the Atlantic with the silicic volcanics of the Tobifera Formation. However, recent geochemical work on the Tobifera Formation suggest an origin by continental crust anatexis in a volcano-tectonic rift zone related to upper mantle diapirism, whereas an island arc origin is favoured for at least the andesitic and basaltic components of the Hardy Formation. Therefore, the geology of Peninsula Hardy as presented here, confirms early assumptions of the splitting apart of a Middle–Upper Jurassic volcanic terrain along the Pacific margin of South America during the generation of a marginal basin. The spreading axis of the latter seems to have been located at the boundary of two somewhat overlapping petrotectonic assemblages: and island arc on the Pacific side and a silicic volcano-tectonic rift zone towards the Atlantic. A probably Cenozoic volcanic complex discordantly overlies the Yahgan and Hardy formations.

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